Phosphonylation alkynes

Addition of phosphonyl radicals onto alkenes or alkynes has been known since the sixties [14]. Nevertheless, because of the interest in organic synthesis and in the initiation of free radical polymerizations [15], the modes of generation of phosphonyl radicals [16] and their addition rate constants onto alkenes [9,12,17] has continued to be intensively studied over the last decade. Narasaka et al. [18] and Romakhin et al. [19] showed that phosphonyl radicals, generated either in the presence of manganese salts or anodically, add to alkenes with good yields. 

Esters of a-diazoalkylphosphonic acids (95) show considerable thermal stability but react with acids, dienophiles, and triphenylphosphine to give the expected products. With olefinic compounds in the presence of copper they give cyclopropane derivatives (96), but with no such compounds present vinylphosphonic esters are formed by 1,2-hydrogen shift, or, when this route is not available, products such as (97) or (98) are formed, resulting from insertion of a carbenoid intermediate into C—C or C—H bonds. The related phosphonyl (and phosphoryl) azides (99) add to electron-rich alkynes to give 1,2,3-triazoles, from which the phosphoryl group is readily removed by hydrolysis. 

Similar reactions can lead to the formation of two P-C bonds. For example, Pd-catalyzed addition of 7 (a privileged substrate which is often more reactive than other H-phosphonates) to terminal alkynes led to dehydrogenative double cis phosphonylation (Scheme 9). A Pd(II)/Pd(IV) cycle was proposed. Reaction of [Pd(allyl)Cl]2 with 7 gave chloro-bridged dimer 8. Alkyne insertion into the Pd-P bond was then proposed to give alkenyl intermediate 9. P-H oxidative addition would then yield hydride 10, whose reaction with 7 was proposed to lead to P-C bond formation and loss of H2 [18]. 

Photochemically generated phosphonyl radicals are effeetive reducing agents for Cu VCu reduction in copper complexes. It has been shown that the obtained copper(i) species can rapidly catalyse atom transfer radical polymerisation and azide-alkyne cycloadditions in mild conditions, i.e. at ambient temperature and humidity, under an air atmosphere. 

A perfluoroacetylenephosphonate was prepared that can provide access to a number offluoroalkylated and phosphonylated quinolines (Scheme 55). The reaction combines ort/zo-aminoarylketones with perfluoroacetylene-phosphonates in a regioselective manner and is very sensitive to changes in temperature, solvent polarity, and the base used. The reaction failed to proceed in the presence of any of the typical Tewis acids employed in quinoline syntheses. Lower polarity and lower temperatures seemed to be favored for high isolable yields. When the fluorinated alkyne is varied, it appears that... 

The addition of phosphorus pentachloride to alkenes and alkynes yields complexes of the type RPClj PClg, which, when treated with sulphur dioxide, will give phosphonyl chlorides (6.197). Hydrolysis of the aluminium trichloride complexes (6.151) and (6.152) will also give phosphonyl or phosphinyl halides (6.198). 

YA(j 14] Yagci Y, Tasdelen M.A., Jockusch S., Reduction of Cu(ll) by photochemically generated phosphonyl radicals to generate Cu(l) as catalyst for atom transfer radical polymerization and azide-alkyne cycloaddition click reactions . Polymer, vol. 55, pp. 3468-3474, 2014. 

Nucleophilic addition of 5-substituted tetrazoles (501) to ethynyl-phosphonate (500) proceeded regio- and stereoselectively to yield (Z) p-amino-p-tetrazolylvinylphosphonates (502) and (503) via attack of the N-1 (predominantly) or N-2 atom of the tetrazole at the C-2 atom of the triple bond of the phosphonate (500), respectively (Scheme 149)/ Treatment of p-ketophosphonates (504) with terminal alkynes (505) in the presence of an rhenium catalyst and under neutral conditions afforded 2i -l,2-oxaphosphorin 2-oxides (507). The reaction proceeded via cleavage of a C-C a-bond of the p-ketophosphonate (504), regio- and stereoselective insertion of the allq ne (505), followed by cyclisation of the resulting 5-phosphonyl a,p-unsaturated ketone (506) (Scheme 150). ... 

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